Installation and oceanographic relevance of a long-term underwater multi-sensors cabled observatory in Adélie land

In Antarctica, the seaward flow of sea ice explains the trends observed since 2015: stratification, cooling at the surface and warming at greater depths. The coastal waters of Adelie Land, in addition to their benthic biodiversity and the presence of numerous colonies of seabirds and marine mammals, show a role in the formation of deep waters, with strong variability in their productivity and salinity under the control of ice dynamics. This same ice, with its key role in controlling light and salinity, steers underwater living conditions, showing variations on all time and space scales. In an environment where oceanographic measurements are difficult and costly, and navigation is often perilous, we propose to monitor the physical and biological parameters that condition life in the coastal waters of Adelie Land.

The main objectives of OBAMMAA project are (1) to deploy (to demonstrate the feasibility and relevance of) a wired multi-probes marine observatory with innovative acoustical sensors in coastal Antarctic waters, Terre Adélie, (2) to compare physical measurements made by low-cost micro-AUVs (3D discrete sampling) with those made by the cabled observatory (1D continuous), (3) to map both sea bottoms  properties (bathymetry, habitats, biodiversity) and water properties around the Petrel Island (French: Île des Pétrels) using micro-AUV we are developing in patership with SEABER and MARBEC-Project SEAMAP (https://seaber.fr/) and (4) to quantify for the first time the impact of anthropogenic noises on benthic fauna in a well described coastal ecosystem. On the first year, we will deploy a multi-sensors cabled observatory (acoustics, temperature, salinity, water velocity, oxygen, chlorophyll a, light, underwater time-lapse camera) in shallow water (~20 m), southwest of Petrel Island, in an area protected from icebergs scouring. An aerial time-lapse camera will be installed on a short pole at/near the Jakobsen Rocher to monitor the sea ice presence/dynamics and seabird activities around the underwater observatory site. As the system has been designed to be flexible, we will be able to add sensors of interest to the scientific community in the following years. The control unit will be hosted in a shelter (Ionospheric Mast – “Mât-Iono”), which has a heated room with 220 V electric power and a communication wire connected to the main building of the DDU base. To better describe the acoustic environment of the archipelago, we will perform additional passive acoustic measurements using autonomous recorders in other locations, both from holes in the ice and during summer cruises when the archipelago is free of sea-ice. The data acquired from the cabled observatory will be stored in the Antarctic research station Dumont d’Urville (DDU), but also transferred to (mainland) France using the IPEV communication system. To do so, the acoustic data will be processed in real time within the observatory, and only a flexible selection of processed data will be transmitted, transforming the system into a “smart-sensor”. Data processing will be basic in the first year, and gradually complexified to benefit an interdisciplinary team of end-users (glaciologists, marine ecologists, ornithologists, physical oceanographers, biogeochemists…). Last but not least, we will also take advantage on our time on the field to perform behavior studies on benthic molluscs (impact of noise) and additional physical measurements deploying a pack of micro-AUV (SCAN, Echosound, eDNA sampler, video, CTD and PAM).